Conventional surface mount processing materials, equipment, and methods are incapable of adequately providing a reliable high density surface mountable pin grid array connector. Presently, surface mount technology includes mounting substrates or circuit board carriers by using a small volume of solder paste or flux to solder connector pins directly to the cartridge substrate using conventional stencil printing. This limited solder volume may not be enough to overcome coplanarity or flatness problems with the pin heads or the substrate. Substrates may be warped, or pin heads may not be uniform, or may not be placed properly. This can lead to inconsistencies in the mounting process, which given the stress applied to many circuit boards in the course of their lifetime, may weaken and even break joints, leading to failure of the board, and to potential costly problems with other equipment relying on the board.
The limited solder volume of the present technology leads to a board connection which has a tendency to not be able to overcome the flatness, or coplanarity, variations in connector pin heads or of the substrate to which the connector pins are being attached. Also, the limited solder volume leads to an increased likelihood of mechanical failure of joints in an application environment.
Further, misregistration and placement inaccuracy of components onto a surface mount assembly with low solder volume may cause more problems. More specifically, reflow of a small volume of solder may lead to problems with placement accuracy of a surface mount assembly with respect to the connector. Variations in pin heads and warpage of the substrate of the connector decrease tolerance to any inconsistencies and differences between parts. This can lead to decreased yield and manufacturability of connectors or circuit board carriers. Problems may occur in centering a connector or other board to be soldered to a surface mount assembly due to misregistration or placement inaccuracies. Reflowing a small amount of solder may allow for further buildup of errors.
An additional problem with conventional surface mount technology is reflowing to perform a surface mount connection. During reflow of the low solder volume board, the board solder, used for attaching the circuit board carrier to a surface mount assembly, is melted. The solder holding pins into the carrier also tends to melt, leading to wicking of hole solder over the surface of the pins by capillary action. This melting and wicking of the pin attachment solder can lead to weakening of the joint by further depleting the solder volume of the connector, as well as to an increased effect of variations in flatness of the pin heads or the substrate.
Current connector pins often use an interference type fit structure on the pin. This interference type fit structure may take many forms, such as barbs or other protrusions from the pin which are designed to allow the pin to be press fit into a through hole or via in a circuit board or the like, to be held temporarily until the pins can be soldered into the through hole or via. Such interference fit pins do not deter wicking of the hole solder over the surface of the pin. Depletion of the solder in the hole has been described above. The wicking can even allow solder to flow over and around a shoulder situated on the pin and positioned at the end of a hole.